﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.IO;
using System.Security.Cryptography;

namespace TrainingCenterSystem.Utils
{
    public class StringEncryption
    {
        public static string EncryptString(string clearText, string password)
        {
            // First we need to turn the input string into a byte array.
            byte[] clearBytes = System.Text.Encoding.Unicode.GetBytes(clearText);

            
            // Then, we need to turn the password into Key and IV
            // We are using salt to make it harder to guess our key using a dictionary attack -
            // trying to guess a password by enumerating all possible words.

            PasswordDeriveBytes pdb = new PasswordDeriveBytes(password,
                        new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            

            // Now get the key/IV and do the encryption using the function that accepts byte arrays.
            // Using PasswordDeriveBytes object we are first getting 32 bytes for the Key
            // (the default Rijndael key length is 256bit = 32bytes) and then 16 bytes for the IV.
            
            // IV should always be the block size, which is by default 16 bytes (128 bit) for Rijndael.
            // If you are using DES/TripleDES/RC2 the block size is 8 bytes and so should be the IV size.
            // You can also read KeySize/BlockSize properties off the algorithm to find out the sizes.

            byte[] encryptedData = Encrypt(clearBytes, pdb.GetBytes(32), pdb.GetBytes(16));

            
            // Now we need to turn the resulting byte array into a string.
            // A common mistake would be to use an Encoding class for that. It does not work
            // because not all byte values can be represented by characters.
            // We are going to be using Base64 encoding that is designed exactly for what we are
            // trying to do.

            return Convert.ToBase64String(encryptedData);
        }

        public static byte[] Encrypt(byte[] clearData, byte[] Key, byte[] IV)
        {
            // Create a MemoryStream that is going to accept the encrypted bytes
            MemoryStream ms = new MemoryStream();

            // Create a symmetric algorithm.
            // We are going to use Rijndael because it is strong and available on all platforms.
            // You can use other algorithms, to do so substitute the next line with something like
            //                      TripleDES alg = TripleDES.Create();

            Rijndael alg = Rijndael.Create();
                        
            // Now set the key and the IV.
            // We need the IV (Initialization Vector) because the algorithm is operating in its default
            // mode called CBC (Cipher Block Chaining). The IV is XORed with the first block (8 byte)
            // of the data before it is encrypted, and then each encrypted block is XORed with the
            // following block of plaintext. This is done to make encryption more secure.
            // There is also a mode called ECB which does not need an IV, but it is much less secure.

            alg.Key = Key;
            alg.IV = IV;

            // Create a CryptoStream through which we are going to be pumping our data.
            // CryptoStreamMode.Write means that we are going to be writing data to the stream
            // and the output will be written in the MemoryStream we have provided.

            CryptoStream cs = new CryptoStream(ms, alg.CreateEncryptor(), CryptoStreamMode.Write);
            
            // Write the data and make it do the encryption

            cs.Write(clearData, 0, clearData.Length);
            
            // Close the crypto stream (or do FlushFinalBlock).
            // This will tell it that we have done our encryption and there is no more data coming in,
            // and it is now a good time to apply the padding and finalize the encryption process.

            cs.Close();
            
            // Now get the encrypted data from the MemoryStream.
            // Some people make a mistake of using GetBuffer() here, which is not the right way.

            byte[] encryptedData = ms.ToArray();
            
            return encryptedData;
        }

        private static byte[] EncryptString(byte[] clearText, byte[] Key, byte[] IV)
        {
            MemoryStream ms = new MemoryStream();
            Rijndael alg = Rijndael.Create();
            alg.Key = Key;
            alg.IV = IV;
            CryptoStream cs = new CryptoStream(ms, alg.CreateEncryptor(), CryptoStreamMode.Write);
            cs.Write(clearText, 0, clearText.Length);
            cs.Close();
            byte[] encryptedData = ms.ToArray();
            return encryptedData;
        }

        public static byte[] Decrypt(byte[] cipherData, byte[] Key, byte[] IV)
        {
            // Create a MemoryStream that is going to accept the decrypted bytes
            MemoryStream ms = new MemoryStream();

            // Create a symmetric algorithm.
            // We are going to use Rijndael because it is strong and available on all platforms.
            // You can use other algorithms, to do so substitute the next line with something like
            //                      TripleDES alg = TripleDES.Create();

            Rijndael alg = Rijndael.Create();

            
            // Now set the key and the IV.
            // We need the IV (Initialization Vector) because the algorithm is operating in its default
            // mode called CBC (Cipher Block Chaining). The IV is XORed with the first block (8 byte)
            // of the data after it is decrypted, and then each decrypted block is XORed with the previous
            // cipher block. This is done to make encryption more secure.

            // There is also a mode called ECB which does not need an IV, but it is much less secure.

            alg.Key = Key;
            alg.IV = IV;
            

            // Create a CryptoStream through which we are going to be pumping our data.
            // CryptoStreamMode.Write means that we are going to be writing data to the stream
            // and the output will be written in the MemoryStream we have provided.

            CryptoStream cs = new CryptoStream(ms, alg.CreateDecryptor(), CryptoStreamMode.Write);
            
            // Write the data and make it do the decryption

            cs.Write(cipherData, 0, cipherData.Length);
            
            // Close the crypto stream (or do FlushFinalBlock).
            // This will tell it that we have done our decryption and there is no more data coming in,
            // and it is now a good time to remove the padding and finalize the decryption process.

            cs.Close();



            // Now get the decrypted data from the MemoryStream.
            // Some people make a mistake of using GetBuffer() here, which is not the right way.

            byte[] decryptedData = ms.ToArray();
            
            return decryptedData;
        }





        // Decrypt a string into a string using a password

        //    Uses Decrypt(byte[], byte[], byte[])

        public static string Decrypt(string cipherText, string Password)
        {
            // First we need to turn the input string into a byte array.
            // We presume that Base64 encoding was used
            byte[] cipherBytes = Convert.FromBase64String(cipherText.Replace(" ","+"));

            // Then, we need to turn the password into Key and IV
            // We are using salt to make it harder to guess our key using a dictionary attack -
            // trying to guess a password by enumerating all possible words.

            PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,
                        new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
                        
            // Now get the key/IV and do the decryption using the function that accepts byte arrays.
            // Using PasswordDeriveBytes object we are first getting 32 bytes for the Key
            // (the default Rijndael key length is 256bit = 32bytes) and then 16 bytes for the IV.

            // IV should always be the block size, which is by default 16 bytes (128 bit) for Rijndael.
            // If you are using DES/TripleDES/RC2 the block size is 8 bytes and so should be the IV size.
            // You can also read KeySize/BlockSize properties off the algorithm to find out the sizes.

            byte[] decryptedData = Decrypt(cipherBytes, pdb.GetBytes(32), pdb.GetBytes(16));
            
            // Now we need to turn the resulting byte array into a string.
            // A common mistake would be to use an Encoding class for that. It does not work
            // because not all byte values can be represented by characters.

            // We are going to be using Base64 encoding that is designed exactly for what we are
            // trying to do.

            return System.Text.Encoding.Unicode.GetString(decryptedData);            
        }

        // Decrypt bytes into bytes using a password
        //    Uses Decrypt(byte[], byte[], byte[])
        public static byte[] Decrypt(byte[] cipherData, string Password)
        {
            // We need to turn the password into Key and IV.
            // We are using salt to make it harder to guess our key using a dictionary attack -           
            // trying to guess a password by enumerating all possible words.

            PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,

                        new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            
            // Now get the key/IV and do the Decryption using the function that accepts byte arrays.
            // Using PasswordDeriveBytes object we are first getting 32 bytes for the Key
            // (the default Rijndael key length is 256bit = 32bytes) and then 16 bytes for the IV.

            // IV should always be the block size, which is by default 16 bytes (128 bit) for Rijndael.
            // If you are using DES/TripleDES/RC2 the block size is 8 bytes and so should be the IV size.
            // You can also read KeySize/BlockSize properties off the algorithm to find out the sizes.

            return Decrypt(cipherData, pdb.GetBytes(32), pdb.GetBytes(16));            
        }





        // Decrypt a file into another file using a password

        public static void Decrypt(string fileIn, string fileOut, string Password)
        {
            // First we are going to open the file streams
            FileStream fsIn = new FileStream(fileIn, FileMode.Open, FileAccess.Read);
            FileStream fsOut = new FileStream(fileOut, FileMode.OpenOrCreate, FileAccess.Write);
            
            // Then we are going to derive a Key and an IV from the Password and create an algorithm
            PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,
                        new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            
            Rijndael alg = Rijndael.Create();

            alg.Key = pdb.GetBytes(32);
            alg.IV = pdb.GetBytes(16);

            // Now create a crypto stream through which we are going to be pumping data.
            // Our fileOut is going to be receiving the Decrypted bytes.

            CryptoStream cs = new CryptoStream(fsOut, alg.CreateDecryptor(), CryptoStreamMode.Write);
            
            // Now will will initialize a buffer and will be processing the input file in chunks.
            // This is done to avoid reading the whole file (which can be huge) into memory.

            int bufferLen = 4096;

            byte[] buffer = new byte[bufferLen];

            int bytesRead;
            
            do
            {
                // read a chunk of data from the input file
                bytesRead = fsIn.Read(buffer, 0, bufferLen);
                
                // Decrypt it
                cs.Write(buffer, 0, bytesRead);
            } while (bytesRead != 0);
            
            // close everything
            cs.Close(); // this will also close the unrelying fsOut stream
            fsIn.Close();
        }
    }
}
